How to animate a propellor?
If you want to animate it rotating, you move your time to specific frame.
Press I to set a key frame, select rotation from the pop-up window.
Move to another frame (15 frames after the previous frame), rotate the object around it's axis, press I again to set another key frame (select rotation again).  

This will cause it to 'spin' for 15 frames.  Without more details regarding your goal, this is the simplest way to animate.